The present invention generally relates to header structures for TDD (time divisional duplex) systems, and particularly to a wireless transmission method and a wireless transmission system using a time division duplex systems using such header structures.
TDD (time division duplex) systems are well known in the state of the art. As an example the DECT-standard is cited. In time division duplex systems frames are used which comprise a plurality of timeslots. According to the state of the art some of the timeslots of a frame are dedicated for the transmission of data from a base station of the TDD system to mobile stations, which is called downlink channel, and the other timeslots are dedicated to the transmission of information from a mobile station to the base station of the TDD system, which is called uplink channel. One timeslot according to the state of the art is dedicated either for the uplink channel communication or the uplink channel communication.
A typical structure of a known TDD frame is shown in FIG. 2. In FIG. 2 the timeslots used for the transmission of voice data or other data are referenced with TS (traffic slots). Besides these traffic slots (TS) a so-called header is provided. According to the state of the art, the header occupies at least two timeslots, wherein one timeslot is used for a downlink channel header part (DC) and the other timeslot is used for an uplink channel header part. The downlink header part (DC) consists of synchronization information (SYNCH) and broadcast information (GBCCH). The second timeslot occupied by the header is reserved for uplink unsynchronized mobile station access trials (RACH, random access channel).
As the header portion occupies two timeslots of the frame structure of the TDD system, these timeslots cannot be used for example for the transmission of voice data. Thus, the effective bit rate of the transmission is decreased.
It is the object of the present invention to provide an improved header structure for a TDD system providing for an improved effective bit rate and transmission flexibility of the transmission.
The improved header structure furthermore should be advantageously compatible with a so-called OFDM system comprising a plurality of equally spaced sub-carriers.
Still further the improved header structure for the TDD system should be compatible with the well-known GSM standard.
The object of the invention is achieved by means of the features of the independent claims. The depending claims develop further the central idea of the present invention.
According to the present invention therefore a wireless transmission method is provided, wherein data is transmitted in frames according to a time divisional duplex (TDD) system. Each frame thereby comprises a header and a plurality of traffic slots. The header and the traffic slots have the same time duration. According to the present invention one single timeslot is occupied by the header, wherein the header is subdivided into a downlink channel for the transmission of synchronization data and system data from a base station to at least one mobile station, and an uplink channel for the transmission of registration data from at least one mobile station to the base station. According to the present invention therefore the header occupies only one timeslot of a TDD frame. Thus the effective bit rate of the transmission can be enhanced.
Preferably the downlink channel and the uplink channel of the header slot have the same time duration.
The downlink channel can comprise a synchronization channel and at least one broadcast channel for the transmission of cell and/or system data to all or selected mobile stations.
Preferably the synchronization channel comprises at least two identical repeated symbols. These repeated identical symbols can be used for a correlation detection such as to effect frequency and time synchronization of the transmission scheme.
The at least one broadcast channel of the header slot can comprise at least two identical repeated symbols such as to further enhance the efficiency of the correlation detection and to improve the security of the data transmission.
A general broadcast channel can be transmitted in every frame and an optional broadcast channel can be transmitted only when the capacity of the general broadcast channel is not sufficient or when specific data are to be transmitted.
At least for the transmission of the optional broadcast channel of the header slot an OFDM system with a plurality of subcarriers can be used.
At least for the transmission of the synchronization channel of the header slot an OFDM system comprising a plurality of equally spaced subcarriers can be used, wherein the time duration of a symbol of the synchronization channel can be 1/n, n being an integer greater than 1, of the time duration of the symbols and the traffic channel, and only every n-th subcarrier is modulated in the synchronization channel.
The synchronization channel can be comprised of two identical repeated symbols having respectively a time duration of 30 microseconds, wherein a basic subcarrier spacing of 4.167 kHz is used for the OFDM system and only every eighth subcarrier can be modulated in the synchronization channel. Said specific parameters are particularly preferable in view of a compatibility with GSM parameters.
In the optional broadcast channel a subset of subcarriers can be allocated to the transmission of data for a predetermined mobile station. Thereby the advantage of the flexibility of the frequency allocation of the OFDM system can be used, as according to the state of the art always the entire band width is used to transmit broadcast channel data (in single carrier systems).
The time duration of one timeslot can be equal to the time duration of one timeslot according to the GSM standard.
A preferable use of a wireless transmission method as set forth above are indoor applications and low range outdoor applications.
The present invention furthermore relates to a wireless transmission system comprising a basic station and at least one mobile station. The base station and the mobile station are adapted to transmit data in frames according to a time divisional duplex (TDD) system. The header slot occupies only one single timeslot of the frame structure of the TDD system. The header slot and the traffic slots can have the same time duration. Furthermore, the header slot can be subdivided into a downlink channel for the transmission of synchronization data and system data from said base station to said at least one mobile station, and an uplink channel for the transmission of registration data from said at least one mobile station to the base station.
The downlink channel and the uplink channel can have the same time duration.
The downlink channel can comprise a synchronization channel and at least one broadcast channel for the transmission of cell and/or system data to the mobile stations.
The synchronization channel can comprise at least two identical repeated symbols.
The at least one broadcast channel can comprise at least two identical repeated symbols.
The base station and the mobile station (S) can be adapted to use the repeated structure of the synchronization channel and/or the broadcast channel for a frequency and/or time synchronization by means of a correlation detection means.
A general broadcast channel can be provided in every frame and an optional broadcast channel can be only provided when the capacity of the general broadcast channel is not sufficient or when specific data are to be transmitted to dedicated mobile stations.
At least for the transmission of the downlink channel of the header slot an OFDM system comprising a plurality of equally spaced subcarriers can be used.
The time duration of a symbol of the synchronization channel can be 1/n * (subcarrier spacing), n being an integer greater than 1, of the time duration of the symbols and the traffic channel, and only every n-th subcarrier is modulated in the synchronization channel. The synchronization channel can be comprised of two identical repeated symbols having respectively a time duration of 30 microseconds, wherein a basic subcarrier spacing of 4.167 kHz is used for the OFDM system and only every eighth subcarrier is modulated.
The time duration of one timeslot can be equal to the time duration of one timeslot according to the GSM standard.